1. Field of the Invention
This invention relates to an improvement of a lockup control device having a locking up mechanism to connect an input shaft directly with an output shaft in a fluid transmission, such as a torque converter.
2. Description of the Prior Art
In the conventional fluid transmission having such a locking up mechanism as mentioned above, friction and release of a locking up mechanism are controlled on the basis of preset control patterns. For example, the Japanese Patent Application Laying Open Gazette No. 57-184754 discloses control patterns of an automatic transmission including a locking up mechanism control pattern. According to this disclosure, two kinds of pattern, namely, an output demand pattern and a specific fuel consumption priority pattern, are set beforehand and at the time of acceleration demand when the speed of stepping on an accelerator pedal exceeds a set value, an output demand pattern is selected compulsorily to improve accelerability of a vehicle.
Also, the Japanese Patent Application Laying Open Gazette No. 57-33253 discloses a system whereby the number of revolutions of an input shaft and that of an output shaft of a torque conventer are detected and the locking up mechanism is so controlled that when the difference in the number of revolutions between the input shaft and the output shaft in the predetermined specific running area exceeds a target slip quantity, its frictional force becomes larger but while the difference in the number of revolutions is less than the target slip quantity, its frictional force is small and thus the difference in the number of revolutions is adjusted to the target slip quantity.
However, in the engine provided with such fluid transmission as mentioned above, at the deceleration running when the throttle value valve is closed and the engine running state is not in the specific running area where frictional force of the locking up mechanism is controlled, engine brake force works only through the fluid transmission and such engine brake force decreases by slip in the fluid transmission. Therefore, the desired decelerating effect cannot be obtained and a driver does not have a good feeling of deceleration.
It is suggested that in the case where a target slip quantity between an input shaft and an output shaft of a torque converter is set, by setting it variable according to the engine speed (r.p.m.) and the throttle valve opening (for example, small slip quantity for a small throttle valve opening and a large slip quantity for a large throttle valve opening), improvement of accelerating capacity can be made at the accelerating running when the throttle valve opens large due to the torque increasing action of the torque converter. According to this suggestion, since there are cases where acceleration is effected from a small opening of a throttle valve and the normal running is maintained at a large opening of the throttle valve, it is possible to suppress the reduction in specific fuel consumption caused by slip of a torque converter (because at the accelerating running from a small opening of the throttle valve, the locking up mechanism is substantially in direct connection state), but torque increasing action of the torque converter cannot be displayed effectively and accelerating capacity lowers. Also, during the normal running at large opening of the throttle valve, specific fuel consumption worsens due to large slip quantity.
The present invention refers to a fluid transmission provided with a locking up mechanism. The first invention of the present application has for its object to obtain the desired deceleration effect by working as large engine brake force as possible by using a locking up mechanism at the specified decelerating running when the engine load decreases. The second invention of the present application has for its object to plan coexistance of accelerability and specific fuel consumption.
In order to attain the above objects, in the first invention at the decelerating running the locking up mechanism is caused to put out large frictional force so as to prevent decline of engine brake force due to slip of the fluid transmission. In the second invention, the change of engine load is detected and according to such change rate, whether accelerating running or normal running is judged and a target slip quantity is set.
Concretely, the first invention of the present application has as its prerequisite a lockup control device provided with a lockup device to connect an input shaft directly with an output shaft of a fluid transmission and a control means to control friction and release of the lockup device on the basis of a preset lockup control pattern. It has also a load changing state detecting means to detect the changing state of engine load and a lockup control pattern changing means which, when the change rate of load detected by the load changing state detecting means is more than a negative set value, changes the lockup control pattern of the above control means to the direction in which the large friction force area of the lockup device expands.
The second invention of the present application has as its prerequisite a lockup control device of a fluid transmission provided with a lockup device to connect an input shaft directly with an output shaft of a fluid transmission and a control means to control frictional force of the lockup device so that the difference in the number of revolutions (r.p.m.) between the input shaft and the output shaft of the fluid transmission in the set running area becomes a target slip quantity. It has also a load changing state detecting means to detect the changing state of engine load and a target slip quantity changing means to change the target slip quantity of the above control means to the increasing side when the change rate of load detected by the load changing state detecting means is more than a set value.
By the above composition, in the first invention at the decelerating running when the change rate of engine load becomes more than the negative set value, the lockup control pattern is changed and even in the area where the lockup device is cut off at the normal running, the lockup device is controlled to the perfect friction state or to the specified frictional force and therefore, as compared with the case where engine brake force passes through only the fluid transmission, large engine brake force acts and good feeling of deceleration can be obtained. In the second invention, when the change rate of engine load exceeds a set value, it is judged to be the accelerating running and a target slip quantity is changed to the increasing side. Therefore, torque increasing action of the torque converter is dislayed effectively and acceleration capacity is improved.
On the other hand, in the case where the change rate of engine load is less than a set value, it is judged to be the normal running and a target slip quantity is maintained at a set value. If the target slip quantity is set at a small value, good specific fuel consumption can be obtained.
The above objects and novel features of the present invention will be understood more clearly by reading the following description made with reference to the accompanying drawings.